.a {
    width:100px;
    height: 100px;
    background-color: green;
    border-radius: 10px;
}
.b{
    width: 20px;
    height: 20px;
    background-color: red;
    border-radius: 50%;
}
.c{
    width: 100%;
    height: 20px;
    background-color: aquamarine;
}